PerkinElmer combustion tubes are composed of pure fused quartz which is 99% Si02. Fused quartz has been chosen because of its very high purity and low thermal expansion rate. Because we care about your safety, all combustion tubes are pressure-tested to eliminate any tubes which might contain weak spots. In addition, stringent specifications are used to insure that the combustion tubes fit in an airtight connection when placed in the analyzer.